1. Field of the Invention
This invention is both a system and a process for inspecting a plurality of conduits, each of which includes an open end mounted in a manifold. It is particularly useful in inspecting the boiler tubes of a fossil fuel electrical power plant, where each of the tubes has an open end mounted in a cylindrical mud drum.
2. Description of the Prior Art
Systems and processes for inspecting the boiler tubes in fossil fuel steam generators are known in the prior art. Such systems and processes generally involve the shutdown of the boiler, and the construction of an array of scaffolds around the tubes to be inspected. After the scaffolding has been completed, the outside surfaces of the tubes are ultrasonically and visually inspected, and the locations of damaged or corroded sections of these tubes are recorded. The damaged or corroded tube sections are then repaired, the scaffolding disassembled, and the boiler re-fired.
Unfortunately, such prior art systems have a number of shortcomings which have yet to be solved in the prior art. For example, it usually takes about three weeks to build the scaffolding and to complete an inspection of a typical fossil fuel steam boiler when such prior art systems are used. This necessitates three weeks of down time for the electrical generators which are driven by the steam boiler under inspection, which in turn results in a substantial loss of revenues. Additionally, the resulting inspection often fails to locate the sections of some of the tubes which are in need of repair due to the fact that many of the tubes are closely packed together, and take more than one 160.degree. turn throughout their lengths. Hence, some portions of the tubes are simply not visible or accessible to an inspector, regardless of how well positioned the scaffolds are. Also, since only the outside surfaces of these tubes may be inspected with such prior art methods, extensive cracking or corrosion which occurs on the inside of the tubes will not be detected by the inspectors unless it has worked its way completely through the tubes.
While robotically-movable eddy current probes for inspecting the inside walls of heat exchange tubes of nuclear steam generators are also known in the prior art, the systems which employ such probes would not be functional in a fossil fuel boiler for a number of reasons. First, the heat exchange tubes in nuclear steam generators each have an open end which is mounted in a flat tubesheet which may be accessed through a manway in the primary side of the generator. While the boiler tubes in fossil fuel generators likewise have an open end which is accessible through a manway, the open ends of such tubes are mounted around the axis of a cylindrical mud drum in a spoke-like pattern which is frequently irregular. Moreover, the inner dimensions of such mud drums (i.e., 40 feet long and only 14 inches in diameter throughout much of its length) would not give a probe operator or any known robotic system a sufficient amount of room to crawl through the drum and to sequentially insert an eddy current probe throughout each of the open ends of the tubes. And even if the mud drum had a larger diameter throughout its entire 40 foot length, the time it would take to snake such a probe either manually or robotically up through each of the 220-foot-long, zig-zagging tubes would be prohibitive, if it could be accomplished in this manner at all.
Accordingly, there is clearly a need for some sort of inspection system and process which is capable of inspecting the boiler tubes in a fossil fuel power plant with a minimum amount of time and effort, and a maximum amount of reliability and accuracy. Such a system should be capable of inspecting each of the tubes from its inside wall, so that damage caused by internal corrosion, pitting, or cracking could be repaired before it had an opportunity to completely penetrate the tube walls. Ideally, such a system should be capable to inspecting each boiler tube throughout its entire length, regardless of its position with respect to adjacent boiler tubes, and regardless of how many bends it may have along its length.